A variety of gas-phase techniques for depositing materials on a substrate are known in the art, including physical vapor deposition (PVD) based techniques such as evaporation, sputtering, molecular beam epitaxy (MBE), and pulsed laser deposition (PLD), and a wide variety of chemical vapor deposition (CVD) based techniques, including atomic layer deposition (ALD). These techniques are ubiquitous in the development of novel materials and films that have a wide range of applications from consumer electronics to biology or medicine, from architectural engineering to aerospace. Both PVD and CVD based techniques may include exposing the substrate to an atomic or molecular species at a set of processing parameters that are selected based on the deposition technique to be used, the material to be deposited, and the substrate upon which the material is to be deposited.
For example, FIGS. 1A-1B schematically illustrate structures that may be formed during a previously known gas-phase material deposition technique. As illustrated in FIG. 1A, substrate 110 may be exposed to an atomic or molecular species 120 that is in the gas phase. In the evaporation and MBE techniques, such gas phase atomic or molecular species 120 may be formed by heating and evaporating a material using a variety of known power sources, including a resistive or radiative heater or an electron beam. The PLD technique is similar, but irradiates a material using a pulsed laser to generate gas phase atomic or molecular species 120. In the sputtering technique, such gas phase atomic or molecular species 120 may be formed by bombarding a material with energetic particles so as to liberate molecules of the material into the gas phase; the energetic particles may be generated using a variety of known sources, including a plasma, an ion source, a particle accelerator, or a radioactive material. In the CVD and ALD techniques, such gas phase atomic or molecular species 120 may be stored separately in gaseous form and introduced to a reaction chamber that contains the substrate; the species optionally may be activated using a suitable source, such as with a plasma, combustion, or thermal decomposition.
As illustrated in FIG. 1A, gas phase atomic or molecular species 120 may adsorb onto substrate 110, forming adsorbed atomic or molecular species 120′. Upon such adsorption, atomic or molecular species 120′ may form a molecular bond with substrate 110, e.g., a covalent or ionic bond, or a bond based on dipole-dipole interactions, London dispersion force, or hydrogen bonding. Upon such bonding with substrate 110, atomic or molecular species 120′ may directly form material 140 disposed on substrate 110, as illustrated in FIG. 1B, or may first undergo a further chemical reaction, e.g., with substrate 110, with another atomic or molecular species 120′ adsorbed to substrate 110, or with another gas phase atomic or molecular species 120, to form material 140 illustrated in FIG. 1B. In many situations, the adsorbed atomic or molecular species 120′ may move along the surface to find the right accommodation (e.g., site on substrate 110, or another gas phase or adsorbed atomic or molecular species) for the ultimate reaction to occur. At the macroscopic level, the processing parameters used during a given material deposition technique may include the type and power level of any source selected to assist with generating or activating gas phase atomic or molecular species 120; any electrical bias that may be applied to substrate 110; any heating or cooling that may be applied to gas phase atomic or molecular species 120 or to substrate 110; the flow rate or concentration of gas phase atomic or molecular species 120; the pressure or partial pressure of gas phase atomic or molecular species 120; and the amount of time with which substrate 110 is exposed to gas phase atomic or molecular species 120.
At the microscopic level, the energy barrier that may be required to convert gas phase atomic or molecular species 120 illustrated in FIG. 1A into material 140 illustrated in FIG. 1B may be far lower than the total amount of energy provided by the processing parameters. In this regard, at the microscopic level, substrate 110 may be viewed as an energy “sink” toward which atomic or molecular species 120 is attracted, and additional energy may be applied to “agitate” adsorbed atomic or molecular species 120′—that is, to enhance the mobility of species 120 on substrate 110—to convert species 120′ into material 140. The conversion of species 120 to material 140 thus may be considered to have two different types of energy deficits, the first arising from the particular chemical reactivity of atomic or molecular species 120, and the second being of a more general thermodynamic and kinetic nature.
The processing parameters may nominally provide the amount of energy that may be required at the microscopic level to overcome both the first and second types of energy deficits. However, such processing parameters may be applied at the macroscopic or “bulk” level and thus applied to the entirety of substrate 110 and to all gas phase species 120 and all adsorbed species 120′. For example, as illustrated in FIGS. 1A-1B, substrate 110 may be disposed on heater 130 that heats substrate 110 to a temperature sufficient to enhance the mobility of absorbed species 120′ to convert such species into material 140. However, such bulk heating may produce a number of engineering constraints that may limit the type of material 140 that may be deposited on a particular substrate 110. Specifically, the material from substrate 110 is made, including the materials of any structures buried therein, must be compatible with the bulk heating temperature used; while the substrate is maintained at the bulk heating temperature, other objects in the reaction chamber preferably are kept sufficiently cool to inhibit contamination; and supporting hardware to maintain substantially uniform heating, cooling, or temperature stability must be provided to maintain uniform growth of material 140 on substrate 110. In particular, elevated temperatures may cause materials buried within substrate 110 to diffuse into each other or into substrate 110, thus damaging the materials.
Thus, what is needed is a way to enhance mobility of adsorbed atomic or molecular species on a substrate, while reducing the bulk temperature of the substrate.